Method of producing electronic components, corresponding electronic component

ABSTRACT

A method of producing electronic components including at least one circuit having coupled therewith electrical connections including metallic wire bondable surfaces encased in a packaging, the method including bonding stud bumps, in particular copper stud bumps, at determined areas of said wire bondable surfaces.

BACKGROUND Technical Field

The description relates to electronic components.

One or more embodiments may apply to producing so-called lead frames inelectronic components such as, e.g., integrated circuits (ICs).

Description of the Related Art

Electronic components such as integrated circuits (ICs) may include oneor more electronic circuits (e.g., a chip or “die”). These circuits(die) may be encased in a package and possibly arranged on a die pad.The package may include a plastics or ceramic packaging (e.g., a moldingcompound or MC), with die pads connected to pins of the package, withthe die sealed within the package and electrically conductive wires(e.g., gold) connecting the pads to the pins. As a plastic packaging themolding compound is typically represented by an organic resin, e.g.,epoxy resin, while the compound can contain other materials such asfiller material.

Such wires were once attached by hand. In present-day technology thattask is performed by machines, leading to a lead frame (LF), a set ofmetal leads that extend outside the package/housing to form electricalconnection pins for the component.

Lead frames may be produced with a variety of processes.

For instance, lead frames may be etched, e.g., by photolithographicprocesses, by using light to transfer a geometric pattern from aphoto-mask onto a light-sensitive, chemical “photoresist” layerdeposited on a metallic strip. Once developed, the resist layer may bechemically removed from all those areas not affected by the exposurepattern and a photo mask remains on the metal surface to protect locallythe strip from the etching action of, e.g., an acid flow.

Lead frames may also be stamped by creating a frame design on a strip bythe progressive action of plural punches that remove material from thestrip by mechanical action.

Packages used in automotive applications desire a continuous improvementin terms, of adhesion of the package adhesion, i.e., resin or moldingcompound adhesion, with the lead frame, for this reason standard silverplated lead frames have been replaced with pre-plated rough finishing,in particular of copper.

Pre-plated rough finishing are however characterized by a cost that isminimizing final margin on the final product. Moreover, pre-plated roughfinishing are presenting weakness on solderability assessment.

It is known to use solution which involve deposition of an Ag (silver)spot or of an Ag ring on the lead frame.

In this regard in FIG. 1 it is shown an electronic component 10including lead frame 11 in the form of a bare copper frame on which anAg spot 12 is plated as indicated by the diagonal lines. The Ag spot 12is plated in the region of a pad 14 of the lead frame 11, on which achip, not shown in FIG. 1, is glued, including also the region of aground ring 17 of the lead frame 11 and the region of leads 13,specifically the terminal of portion the leads 13 towards the pad 14. Asmentioned, alternatively the Ag plating can be performed only on theregion of such ring 17 and of such leads 13, leaving without silverplating the pad 14.

As mention, in the final packaging the lead frame supporting the chip isincluded in a molding compound.

The Ag spot or Ag ring solution, as the silver plated surfaces ingeneral for reason tied to the chemical affinity and the roughnessproperties, is characterized by a very poor adhesion with the moldingcompound. In particular measurements of the evolution of delaminatedareas under thermo-mechanical stresses indicates that areas of maximumweakness are located around the die, delamination appearing on the diepad and proceeding until the ground ring, where are present wires forthe wire bonding, going through ground ring supports.

This is shown in the drawing of FIGS. 2A-2D, which schematizes theresult of thermo-mechanical Scanning Acoustic Microscope (SAM)measurements. FIG. 2A shows a lead frame 11 with a pad 14 and a die 18on the pad. In FIG. 2A is shown a delamination region 19 a in the diepad 14 near a corner. In FIG. 2B, which pertains to a subsequent timeinstant, the delamination region 19 b includes the four corner of thepad 14. In FIG. 2C then a delamination region 19 c includes the frameregion between the pad 14 and the ring 17. In FIG. 17D the delaminationregion 19 c includes ring delamination region 19 d.

For this reason wide Ag plating surfaces are considered as weaknessareas in term of delamination due to poor mechanical and chemicaladherence with resin.

BRIEF SUMMARY

One or more embodiments may provide improvements in producing leadframes for electronic components capable of overcoming one or moredrawbacks outlined in the foregoing.

One or more embodiments may refer to a corresponding component (e.g., amicroelectronic component such as an integrated circuit).

The claims are an integral part of the disclosure of one or moreexemplary embodiments as provided herein.

One or more embodiments is directed to a method of producing electroniccomponents including at least one circuit having coupled therewithelectrical connections including metallic wire bondable surfaces encasedin a packaging, the method including bonding stud bumps, in particularcopper stud bumps, at determined areas of said wire bondable surfaces.

One or more embodiments may involve that said determined areas are areasidentified as preferential in the delamination propagation.

One or more embodiments may involve identifying determined areas(preferential in the delamination propagation by thermo-mechanicalsimulations estimating said delamination of the of the wire bondablesurfaces, in particular a lead frame or by performing a measurement ofsaid delamination, in particular by SAM analysis.

One or more embodiments may involve that said wire bondable surfacesinclude metallic wire bondable surfaces of a BGA (Ball Grid Array) basedintegrated circuit, in particular bond fingers and/or metal rings

One or more embodiments may involve that the wire bondable surfacesinclude a lead frame of electrically conductive material, the methodincluding the bonding stud bumps at determined areas of the circuit

One or more embodiments may involve that the lead frame is a lead frameincluding a metal plating, in particular silver plating, over an areaincluding a pad and a ground ring of the lead frame or including theground ring only.

One or more embodiments may involve including placing one more studbumps in one or more determined area corresponding to a down set of barsof the lead frame.

One or more embodiments may involve bonding said stud bumps on saidground ring of the lead frame only, or on said pad of the lead frameonly, or both on said ground ring and said pad of the lead frame.

One or more embodiments may involve further including encasing in apackage comprising a molding compound said circuit.

One or more embodiments may involve including attaching a die of saidcircuit to said pad and performing a wire bonding operation, encasing ina package comprising a molding compound the circuit attached to the leadframe.

Embodiments described herein include an electronic component, preferablyan integrated circuit, including at least one circuit or die (18)produced with the method of any of the embodiments described above.

One or more embodiments may offer the following advantages, i.e., thatof improving resin adhesion between the package molding compound and thelead frame thanks to mechanical anchoring realized by the stud bumpslocalized in critical areas of the lead frame.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

One or more embodiments will now be described, purely by way ofnon-limiting example, with reference to the annexed figures, wherein:

FIGS. 1 and 2(A)-2(D) have been already discussed in the foregoing is aschematic representation of one or more embodiments;

FIG. 3 is a schematic plan view of one or more embodiments;

FIGS. 4, 5, and 6 are schematic representation of different embodiments;It will be appreciated that, in order to facilitate understanding theembodiments, the various figures may not be drawn to a same scale.

DETAILED DESCRIPTION

In the ensuing description, one or more specific details areillustrated, aimed at providing an in-depth understanding of examples ofembodiments. The embodiments may be obtained without one or more of thespecific details, or with other methods, components, materials, etc. Inother cases, known structures, materials, or operations are notillustrated or described in detail so that certain aspects ofembodiments will not be obscured.

Reference to “an embodiment” or “one embodiment” in the framework of thepresent description is intended to indicate that a particularconfiguration, structure, or characteristic described in relation to theembodiment is comprised in at least one embodiment. Hence, phrases suchas “in an embodiment” or “in one embodiment” that may be present in oneor more points of the present description do not necessarily refer toone and the same embodiment. Moreover, particular conformations,structures, or characteristics may be combined in any adequate way inone or more embodiments. That is, one or more characteristicsexemplifies in connection with a certain figure can be applied to anyembodiment as exemplified in any other figure.

The references used herein are provided merely for convenience and hencedo not define the scope of protection or the scope of the embodiments.

In general, the solution here described provides, starting from acircuit, such as a chip or die, including metallic wire bondablesurfaces to be encased in a packaging, in particular a lead frame, inparticular with a pre-plated finishing including a standard Ag spot orAg ring, increasing resistance to delamination during thermal cycles byplacing stud bumps, preferably copper bumps on determined areas of themetallic wire bondable surface, in particular on the lead frame, whichare located in critical areas of the frame surface, for example aroundareas identified as preferential in the delamination propagation.

A metallic wire bondable surface is a metal surface on which wirebonding, preferably with copper or gold, can be performed. Preferablysuch metallic wire bondable surface is a silver surface, which usuallyhas also one of the lower adhesion to the mold compound. In variantembodiments said wire bondable surface can be a nickel palladium ornickel phosphorous surface or a surface of an alloy combining nickel,palladium and gold.

In this regard in FIG. 3 it is shown an electronic component 30including a lead frame 21 on which a plurality of critical areas 15 isindicated. As mentioned, critical areas 15 can be identified. Suchcritical areas 15 are more probable to correspond or to be placed nearthe surfaces of the component 30 with the lowest adhesion with respectto the mold compound, i.e., the silver surfaces in the embodimentdescribed, however of course the probability of having delaminationpropagation depends also from the thermo-mechanical properties of thesystem represented by the electronic component 30. A determination ofthe critical areas 15 can be therefore achieved through measurements ofthe evolution of delaminated areas under thermo-mechanical stresses, forinstance performing a SAM analysis of the lead frame 21 and, forinstance, selecting the areas subjected to the greater stress. Thesetypes of analysis are known per se to the person skilled in the art.

In FIG. 3 the critical areas 15 located on a die pad around asemiconductor die (18 in FIGS. 4-6) and in correspondence of down sets22 of ground bars 17. Such down sets 22, as also shown in themeasurements of FIG. 3, are regions prone to promote delaminationprogress versus areas where the wire bonding is present.

As shown in FIG. 3 in each critical area 15 are inserted electricallyand/or thermally conductive, preferably copper, balls or beads, toproduce a plurality of stud bumps 16, preferably copper stud bumps. Invariant embodiments, the stud bumps can be made of gold or silver, thecopper being however a choice of material giving a higher adhesion at alower cost.

Stud bumps 16 are for instance bonded on areas characterized by lowadhesion with molding compound for example silver plated areas of thelead frame 11 in particular in the critical areas 15 by a bondingtechnique which in variant embodiments may correspond to that of thewire bonding, specifically ball bonding. In particular, placing thestuds bump 16 may include a step of lowering a capillary copper wire tothe surface of the lead frame 21, which is preferably heated, then thecapillary copper wire is pushed down and the bonding machine appliesultrasonic energy with an attached transducer. The combined heat,pressure, and ultrasonic energy create a weld between the copper balland the surface of the frame 11. In this case, the wire is then detachedby the ball, for instance simply moving transversally the wire so thatthe wire breaks above the ball, leaving the stud bump 16.

Thus, as shown above, an embodiment of the method here described mayinclude to place one more stud bumps 16 in one or more determined area15 corresponding to a down set of bars, i.e., power bars or supportbars, of the lead frame 21.

The plurality of stud bumps 16 placed in critical areas 15 of thestandard lead frame 11 determines a mechanical anchoring which improvesthe resin, i.e., molding compound adhesion.

In FIG. 4 it is shown an electronic component or package 30′manufactured by steps of the method described above. The electroniccomponent 30′ includes the leadframe 21 on which is placed asemiconductor die 18. The semiconductor die 18 includes an activesurface in which one or more integrated circuits are formed as is wellknown in the art. In FIG. 4 are also shown wires 20 connecting terminalsof the die 18 to the leads 13 of the lead frame 21. The lead frame 21 isbonded with a configuration of bumps 16A which is bonded on the ring 17and a configuration of bumps 16B which is bonded on the pad 14.

FIG. 5 and FIG. 6 show the configuration of the stud bumps 16A on thering 17 (component 30″ in FIG. 5) and 16B on the pad 14 (component 30′″in FIG. 6) separately.

The die 18 and the lead frame 21 of FIGS. 4, 5 and 6, in a step ofpackaging here not shown, are subsequently encased in a package by amolding compound (MC), which anchors to the bumps 16A or 16B or both 16Aand 16B. The package or electronic component includes a die connected topins or leads 21, with the die sealed within the package andelectrically conductive wires (e.g., gold) connecting the pads of thedie to the leads.

In some embodiments, the conductive bumps are only on a ground ring 17of the lead frame, only on the die pad 14 of the lead frame, or only onboth the ground ring 17 and the die pad 14 of the lead frame.

As mentioned, the copper stud bonding can be obtained by employ the ballbonding deposition steps of a standard wire bonding process. By way ofexample a 2.0 millimeters (2.0 mils) Cu wire may be used.

Without prejudice to the underlying principles, the details andembodiments may vary, even significantly, with respect to what isillustrated herein purely by way of non-limiting example, withoutthereby departing from the extent of protection.

Although the solution has been described with reference metallic wirebondable surfaces represented by metallic plated lead frames, thesolution here described can be applied to producing electroniccomponents including one or more circuits including metallic wirebondable surfaces which are then encased in a packaging, this meaningthat in variant embodiments such metallic wire bondable surfaces can beany metal surface of an integrated circuit on which a wire bonding canbe performed. For instance the metallic wire bondable surfaces can bealso represented by a plated surface of the die, so that to enhance theadhesion of the mold compound to the die. Also, the electronic componentmay not include a lead frame, the metallic wire bondable surfacescorresponding to the ones, such as bond fingers and metal rings, of aBGA (Ball Grid Array) based integrated circuit and the stud bumps can bebonded in areas of such bond fingers and/or metal rings.

The electronic component or package may be formed in any order. Forinstance, the semiconductor die may be bonded to the die pad after orbefore the conductive bumps are coupled to the lead frame, such as theperimeter of the die pad and/or the ground ring.

The various embodiments described above can be combined to providefurther embodiments. These and other changes can be made to theembodiments in light of the above-detailed description. In general, inthe following claims, the terms used should not be construed to limitthe claims to the specific embodiments disclosed in the specificationand the claims, but should be construed to include all possibleembodiments along with the full scope of equivalents to which suchclaims are entitled. Accordingly, the claims are not limited by thedisclosure.

1. A device, comprising: a semiconductor die coupled to a die pad of alead frame; conductive bumps on the lead frame; and a package body overthe semiconductor die, the conductive bumps, and portions of the leadframe, wherein the conductive bumps aid in adhering the package body tothe lead frame.
 2. The device of claim 1, wherein the conductive bumpsare on the die pad.
 3. The device of claim 1, wherein the conductivebumps are on a ground ring around the die pad.
 4. The device of claim 3,wherein the ground ring is set downward from leads of the lead frame. 5.The device of claim 1, wherein the lead frame is a copper lead frame,wherein a silver layer is between the copper lead frame and theconductive bumps.
 6. The device of claim 1, wherein the conductive bumpsare on the lead frame at a perimeter of the die pad.
 7. A device,comprising: a semiconductor die coupled to a die pad of a lead frame,the die pad including a plating layer; first conductive anchoring bumpson the die pad; and a package body over the semiconductor die, the firstconductive anchoring bumps, and the die pad, the first conductiveanchoring bumps adhere the package body to the die pad.
 8. The device ofclaim 7, wherein the first conductive anchoring bumps are at a perimeterof the die pad.
 9. The device of claim 7, wherein: the lead frameincludes a ring that extends around the die pad; and second conductiveanchoring bumps are on the ring.
 10. The device of claim 7, wherein theplating layer is silver.
 11. A device, comprising: a lead frameincluding: a die pad having a first surface; a ground ring having asecond surface and being around the die pad; a plurality of leads beingaround the ground ring and around the die pad; a die being coupled tothe first surface of the die pad; a plurality of wires being coupled tothe die and to ones of the plurality of leads, the plurality of wiresextending from the die to ones of the plurality of wires; and aplurality of conductive bumps on only the second surface of the groundring, the plurality of conductive bumps extending away from the secondsurface.
 12. The device of claim 11, wherein ones of the plurality ofwires overlap ones of the plurality of conductive bumps.
 13. The deviceof claim 11, further comprising a molding compound on the lead frame,the die, the plurality of wires, and the plurality of conductive bumps.14. The device of claim 13, wherein the plurality of conductive bumpsare embedded within the molding compound.
 15. The device of claim 11,wherein the plurality of conductive bumps include at least one of acopper material, a silver material, and a gold material.
 16. The deviceof claim 11, wherein the lead frame further comprises a plurality ofdown set portions extending from the die pad to the ground ring.
 17. Thedevice of claim 11, wherein ones of the plurality of wires being coupledto the die and to the ground ring and extending from the die to theground ring.
 18. The device of claim 2, wherein the conductive bumps areonly on the die pad.
 19. The device of claim 3, wherein the conductivebumps are only on the ground ring.
 20. The device of claim 7, whereinthe conductive bumps are only on the die pad.